Traditional cursor control devices for controlling movement of a cursor on the display of an electronic device include arrow keys, function keys, mice, track balls, joysticks, j-keys, touchpads, touch screens, light pens, tablets and other similar devices. Although these traditional cursor control devices are generally satisfactory for many applications, in environments in which the cursor control device must operate in a limited workspace and fit within a specific form factor of an electronic device, such as that of a laptop computer, hand held computer, personal digital assistant (PDA), wireline or wireless telephone, video game or other similar electronic device, traditional cursor control devices do not provide sufficient cursor control accuracy.
For example, conventional touchpads commonly implemented in laptop and hand held computers comprise an array of binary pressure sensors. Each binary pressure sensor outputs a binary signal whose state indicates whether the pressure applied to the pressure sensor is greater than or less than a threshold pressure. From the binary signals, a contact region of the touchpad is identified. The contact region is the region of the touchpad in which the pressure applied by the user's finger is greater than the threshold. The position of the contact region is then computed and is used to determine the position of the cursor on the display. Alternatively, the change between the position of the current contact region and the position of a previous contact region is used to determine a change in the position of the cursor on the display.
However, on most touchpad surfaces, the difference in the static and sliding coefficients of friction between the user's finger and the touchpad surface makes it difficult for the user to control small or precise cursor movements. In general, to move his or her finger relative to the touchpad surface, the user must apply sufficient force to overcome the static coefficient of friction. In many cases, the difference between the static coefficient of friction and the sliding coefficient of friction on the touchpad surface causes the user to apply excessive force and, therefore, “overshoot” the desired finger position on the touchpad surface. As a result, attempts by the user to make small or precise movements of the user's finger relative to the touchpad surface produce unpredictable results in the computation of the location of the centroid of the contact region on the touchpad, and hence in the location of the cursor on the display.
There is therefore a need for the ability to detect the position of an applied pressure with greater precision and resolution.